System for multiple site biphasic stimulation to revert ventricular arrhythmias

ABSTRACT

An anti-reentry apparatus and method for reverting ventricular arrhythmias. Biphasic stimulation is applied at multiple ventricular sites to revert arrhythmias caused by reentry, particularly multiple random reentry. In the preferred embodiment, the first phase of biphasic stimulation is anodal, and is at a maximum subthreshold amplitude. The anodal phase preconditions the myocardium to accept the second phase (cathodal) such that less electrical energy is required to reach the threshold amplitude to produce depolarization. The anodal phase stimulation may have a shape over time that is square wave, ramped, or a series of short square wave pulses. Multiple electrodes located at multiple ventricular sites may be stimulated simultaneously, or they may be sequentially stimulated over time in a manner mimicking the normal progress pattern of cardiac depolarization. The multiple ventricular electrodes may stimulate from internal or external surfaces. One or both ventricles may receive biphasic stimulation from multiple electrodes. The invention also may be practiced with respect to atria.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of PCT application no. PCT/US 99/04695,filed Mar. 4, 1999, pending, which claims priority from U.S. patentapplication Ser. No. 09/035,455, filed Mar. 5, 1998, now U.S. Pat. No.6,067,470. The PCT application Ser. No. PCT/US 99/04695, applicationSer. No. 09/035,455, and U.S. Pat. No. 6,067,470 are each incorporatedby reference herein, in their entirety, for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an anti-reentry apparatus andmethod that can favorably influence the beating of ineffective hearts,especially hearts with pathological conditions that interfere withnormal rhythmicity, electrical conduction, and/or contractility bycausing ventricular fibrillation. The present invention particularlyrelates to an anti-reentry apparatus and method that providessimultaneous or progressive biphasic stimulation at multiple sites inone or both ventricles.

2. Background Information

Heart disease and malfunction is a major killer of men and women inAmerica. A variety of pathologies can affect the beating patterns of aheart, and thereby predispose it to developing ventricular fibrillation.Prior to the occurrence of such a severe and ineffective rhythm,conventional pacemakers can be used to treat, for example, suchdisorders as sino-atrial (SA) node block, A-V block, and multipleindependent sites of contraction in the ventricles (also termed ectopicfoci), which, in the extreme, can lead to life threatening ventricularfibrillation. Conventional pacemakers often will control and prevent therecurrence of ectopic foci by preprogrammed stimulation of (usually) theright ventricle via a single electrode. Some pacemakers also employ asecond electrode that is dedicated to the left ventricle. In addition,conventional pacemakers utilize a range of circuit logic patterns tocounter specific problems that are encountered in the more commonpathologies.

However, conventional single ventricular electrode technologies,including the use of a separate single electrode to each ventricle, failin cases in which ventricular fibrillation has ensued (particularly whenthe fibrillation is due to multiple random reentry), and single sitestimulation does not entrain sufficiently large areas of surroundingtissue to produce the concerted contraction that is necessary foroptimal efficiency in pumping blood. In such cases of ventricularfibrillation from multiple random reentry, the patient is put in gravejeopardy for the basic reason that virtually all of the body functionsdepend on delivery of blood to the tissues in order to supply oxygen andnutrients, and also to carry away metabolic waste products. Failure tocorrect such a condition, where the rhythm is so far from optimal,results in the patient being in substantial danger of dying in a veryshort period of time. Though cardioversion/defibrillation may beemployed, including that preprogrammed in the control logic forautomatic activation in some pacemaker-defibrillators, such protocolstypically require large doses of electrical energy to the patient. Inaddition to producing extreme discomfort and sharp pain, these largedoses of electrical energy often also produce cardiac damage. Thevoltage for standard internal defibrillation/cardioversion is from 150to 800 volts, corresponding to approximately 10-35 joules.

Several approaches to these problems have been disclosed. One approachis to stimulate greater portions of ventricular myocardium by utilizinglarger electrodes so that greater portions of myocardium aresimultaneously stimulated. For example, U.S. Pat. No. 5,411,547 toCausey, III discloses the use of defibrillation electrode patches formore efficient bipolar cardiac stimulation. In addition, the use oflarge, plate-like electrodes for defibrillation and cardioversion iswell known. However, the use of such larger electrodes suffers from theproblem of delivery of large doses of electrical energy that producegreat discomfort to the patient and the possibility of tissue damage.

Yet another approach is to use multiple individual electrodesappropriately placed about the ventricles. For further details, refer tothe following U.S. Pat. Nos. 5,649,966 to Noren et al., 5,391,185 toKroll, 5,224,475 to Berg et al., 5,181,511 to Nickolls et al., and5,111,811 to Smits. Though these patents disclose the use of multipleelectrodes, they do not disclose or suggest their use for gradually (yetquickly) entraining the various reentrant foci that can exist inpathological ventricles by stimulating in a progressive pattern thatmimics the normal wave of depolarization that occurs in the heart.

Thus, a need exists for an anti-reentry apparatus and method that willrequire the use of less electrical current/voltage than is typicallyused for defibrillation and cardioversion in order to decrease thelikelihood, or at least the severity, of tissue damage. A need alsoexists for an anti-reentry apparatus and method that will simultaneouslystimulate greater portions of ventricular myocardium to increase theprobability of ventricular conversion (particularly in the presence ofmultiple random reentry), but with delivery of lower doses of electricalenergy per stimulation, which, consequently, will prolong the life ofthe apparatus's batteries and decrease myocardial soft tissue damage. Aneed also exists for such an anti-reentry apparatus and method that notonly will produce the vitally needed improvement in cardiac pumpingefficiency, but additionally will simultaneously lower the probabilityof tissue damage, and provide greater comfort for the patient. Inaddition, a need exists for an anti-reentry apparatus and method thatprogressively stimulates the ventricles in a manner that mimics thenormal cardiac wave of depolarization, thereby providing rapid controland reversion of cardiac rhythm to a normal beating pattern.

SUMMARY OF THE INVENTION

In view of the foregoing limitations in the art, it therefore is anobject of the present invention to provide an apparatus and method thatmore efficiently and quickly entrains larger areas of myocardium topromote ventricular conversion, particularly in patients suffering fromepisodes of multiple random ventricular reentrant foci that produce, ormay produce, ventricular fibrillation.

It is another object of the present invention to provide an apparatusand method that, while entraining larger areas of myocardium, does sowith smaller doses of electrical energy than typically are used indefibrillation and cardioversion.

It is yet another object of the present invention to provide anapparatus and method that, while entraining larger areas of myocardium,does so by stimulating in a progressive pattern that mimics the normalwave of depolarization of the heart.

It is a further object of the present invention to provide an apparatusand method that, while entraining larger areas of myocardium, does sowith less stress on the heart and greater comfort to the patient.

It is yet another object of the present invention to provide anapparatus and method that, while entraining larger areas of myocardium,does so with less damage to cardiac tissue.

It is yet a further object of the present invention to provide anapparatus and method that, while entraining larger areas of myocardium,also promotes greater myocardial blood pumping efficiency.

It is yet a further object of the present invention to provide anapparatus and method that entrains larger areas of myocardium by usingmultiple electrodes that provide biphasic stimulation.

Pacemakers, which utilize low energy stimulation pulses, constitute aseparate and distinct art from cardioverters/defibrillators, whichutilize stimulation pulses of much larger energy—even when theelectrodes are positioned directly on the heart. Thus, according toconventional practice, more energy is required to entrain the entireheart (cardioversion/defibrillation) than to exogenously employ thetraditional pacemaker that typically utilizes the natural cardiacconducting fibers and/or endogenous pacemaker(s) to control the beatingof a heart that is only slightly “out of synch” relative to the moredangerous rhythmicity disorders that often result in extensivefibrillation.

An intermediate ground is demonstrated by the present invention. Byusing multiple electrodes and applying biphasic stimulation, one or bothventricles may gradually (yet quickly) be entrained to beat morenormally in the face of multiple random reentry, even though thestimulation energy level used is lower than that generally used forcardioversion/defibrillation.

Thus, the present invention accomplishes the above objectives byutilizing multiple electrodes that contact multiple ventricular areas 1)for simultaneous biphasic stimulation, or 2) for progressive biphasicstimulation, that is, the mimicking of the physiological patterns ofelectrical current flows or waves of depolarization in the myocardium.The control circuit logic can activate the multiple site, biphasicventricular stimulation upon the occurrence of A-V block in a patientknown to be susceptible to multiple random ventricular reentrant foci,or upon the direct or indirect sensing of ventricular fibrillation. Forexample, direct sensing of ventricular fibrillation can be based on datafrom multiple ventricular sensing electrodes, and indirect sensing canbe based on any of various functional parameters, such as arterial bloodpressure, size and/or presence of an R wave, rate of the electrogramdeflections, or the probability density function (PDF) of theelectrogram.

The present invention accomplishes the above objectives through the useof multiple site, biphasic ventricular stimulation in one or bothventricles to 1) gradually (yet quickly) entrain and interruptsubstantially all of the multiple random reentrant circuits that arepresent; or, failing that, 2) reduce the number of such reentrantcircuits to a level at which much smaller stimuli may be used than inconventional defibrillation/cardioversion to convert the rhythms to morenormal ones, and thereby produce coordinated and efficient cardiacfunction.

The first and second phases of stimulation consist of an anodal pulse(first phase) followed by a cathodal pulse (second phase). In apreferred embodiment, the first phase of stimulation is an anodal pulseat maximum subthreshold amplitude and for a long duration in order toprecondition the myocardium for subsequent stimulation, and the secondphase of stimulation is a cathodal pulse with a short duration and ahigh amplitude. Additional embodiments of the first phase include, butare not limited to, the use of ramped pulses, a series of short durationsquare wave pulses, anodal pulses that are less than the maximumsubthreshold amplitude, and pulses whose magnitudes decay from aninitial subthreshold amplitude to a lower amplitude, where the shape ofthe decay can be linear or curvilinear. It is to be understood that theuse of the phrase “medium energy” stimulation or pulse refers toelectrical stimulation or electrical pulses in which the magnitude ofthe voltage of the electrical stimulation/pulse is lower in magnitudethan that used in typical defibrillation/cardioversion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1-A depicts a heart with multiple ventricular electrodes that areintroduced via the vena cava.

FIG. 1-B depicts a heart with multiple ventricular electrodes that areconnected to external surfaces of the ventricles, and include a separateelectrode set each for the right and left ventricles.

FIG. 2 is a schematic representation of leading anodal biphasicstimulation.

FIG. 3 is a schematic representation of leading anodal stimulation oflow level and long duration, followed by cathodal stimulation.

FIG. 4 is a schematic representation of leading anodal stimulation oframped low level and long duration, followed by cathodal stimulation.

FIG. 5 is a schematic representation of leading anodal stimulation oflow level and short duration administered in a series, followed bycathodal stimulation.

DETAILED DESCRIPTION OF THE INVENTION

The apparatus and method of the present invention may be understood withreference to FIGS. 1-A, 1-B, and 2 to 5.

Referring to FIG. 1-A, a diagram of the heart is shown connected to venacava 103, and having four chambers: right atrium (RA), left atrium (LA),right ventricle (RV), and left ventricle (LV). Electrode lead 101 isshown feeding into the right ventricle via vena cava 103, the rightatrium, and tricuspid valve 111. Individual electrodes 102, 104, 106,108 and 110 are connected to electrode lead 101, and contact multipleinternal sites of the right ventricle. No set number, or absolute rangeas to the number, of individual electrodes is required to practice thisembodiment of the present invention. A typical range could encompass 2to 30 electrodes, though numbers greater than 30 are also contemplated.In addition, there is no set placement of these electrodes. In apreferred embodiment, 6 or less electrodes are used, 4 in the leftventricle and 2 in the right ventricle. It is noted that stimulation ofthe atria through the practice of the present invention also isenvisioned.

Referring to FIG. 1-B, a similar diagram of the heart is shown in whichtwo sets of multiple electrodes are depicted connected to externalventricular surfaces. Electrode lead 201, connected to individualelectrodes 202, 204, 206, 208 and 210, is shown with the individualelectrodes connected to multiple points on the external surfaces of theright ventricle. Electrode lead 301, connected to individual electrodes302, 304, 306, 308 and 310, is shown with the individual electrodesconnected to multiple points on the external surfaces of the leftventricle.

In alternative embodiments, the locations of the individual electrodesin FIG. 1-A (102, 104, 106, 108 and 110), and in FIG. 1-B (202, 204,206, 208 and 210; and 302, 304, 306, 308 and 310) may 1) follow aregular or relatively regular geometric pattern (e.g., an orthogonal orother patterned grid) so as to cover well the ventricular surfaces inappropriate locations; 2) be localized to a particular ventricular areathat is known or suspected to be a source of random reentry circuits; 3)be randomly placed about the selected ventricular surfaces; and/or 4) beplaced about the ventricular surfaces in a progressive pattern tofacilitate mimicking the normal physiological flow of the depolarizationwave that leads to the most efficient contraction of the particularventricle(s).

The latter progressive stimulation embodiment, which mimics the normalphysiological flow of the normal ventricular depolarization wave,requires that areas closest to (or at) the A-V node be the areas firststimulated during a given beat, and that areas farthest from the A-Vnode—following the normal intrinsic conduction paths—be the last areasto be stimulated. Areas intermediate between these two extremes areappropriately stimulated on a scaled time basis that, again, mimics thenormal intrinsic conduction paths that facilitate the most efficientcardiac contraction.

This progressive stimulation embodiment requires specific knowledge ofthe placement of each electrode relative to each other electrode, aswell as the placement relative to the electrical conduction pathways inthe heart. Thus, it is appropriate to contemplate “classes” ofelectrodes, in which, for example, electrodes are identified orcategorized according to when they are fired. In a simplistic five tiersystem, e.g., the first tier electrodes are designated as the first tobe fired (i.e., the electrodes closest to the A-V node), followedsuccessively (and temporally progressively according to the normalconducting paths) by the second, third, fourth, and fifth tierelectrodes, where the fifth tier electrodes would be the last to befired, and whose locations on the ventricle(s) would correspond to thelast areas to be depolarized in the course of a normal ventricularcontraction/beat. An even simpler (i.e., two, three or four) tieredsystem may be used, or one more complex (i.e., one with greater than 5tiers, or with any other basis of electrode placement, such as ahoneycomb-like array in a particular area with a known or suspectedpathology as to rhythmicity, reentry, conduction, contractility, etc.).Furthermore, multiple electrodes within a given tier may be numbered orotherwise distinctly identified so that the practitioner may test anduse electrodes with respect to known locations in the heart, forexample, to anticipate and/or bypass an area of electrical blockage.This type of embodiment would require the use of multiple, smallelectrodes pulsed in a physiologic sequential fashion. In application toatria, electrodes are progressively placed from close to the SA node(first to be fired) to close to the AV node (last to be fired),mimicking the normal intrinsic conduction paths.

Bypassing an area of electrical blockage is also anticipated by thepresent invention, and can be effected by first identifying such areas,for example, by determining myocardial resistance values betweenelectrodes. Electrical pulses then are routed to those myocardial areaswith appropriately low resistances, following as closely as possible thelines of conduction of the normal intrinsic conduction paths.Communication of, and control of, measurements of resistance betweenelectrodes, as well as developing a bypass protocol for a particularpatient, can be effected by an external computer. The external computercan communicate with the pacemaker by any convenient method, forexample, radiotelemetry, direct coupling (as by connecting to anexternal wire from the pacemaker to the surface of the skin of thepatient), etc.

FIGS. 2 through 5 depict a range of biphasic stimulation protocols.These protocols have been disclosed in U.S. patent application Ser. No.08/699,552 (filed Aug. 19, 1996 by the inventor of the presentapplication), which is incorporated by reference herein, in itsentirety, for all purposes.

FIG. 2 depicts biphasic electrical stimulation in which a firststimulation phase comprising anodal stimulus 202 is administered withamplitude 204 and duration 206. The first stimulation phase is followedimmediately by a second stimulation phase comprising cathodal stimulus208, which is of equal intensity and duration to those of anodalstimulus 202.

FIG. 3 depicts biphasic electrical stimulation wherein a firststimulation phase comprising low level, long duration anodal stimulation302 having amplitude 304 and duration 306 is administered. This firststimulation phase is immediately followed by a second stimulation phasecomprising cathodal stimulation 308 of conventional intensity andduration. In an alternative embodiment of the invention, anodalstimulation 302 is at maximum subthreshold amplitude. In yet anotheralternative embodiment of the invention, anodal stimulation 302 is lessthan three volts. In another alternative embodiment of the invention,anodal stimulation 302 is a duration of approximately two to eightmilliseconds. In yet another alternative embodiment of the invention,cathodal stimulation 308 is of a short duration. In another alternativeembodiment of the invention, cathodal stimulation 308 is approximately0.3 to 1.5 milliseconds. In yet another alternative embodiment of theinvention, cathodal stimulation 308 is of a high amplitude. In anotheralternative embodiment of the invention, cathodal stimulation 308 is inthe approximate range of three to twenty volts. In yet anotheralternative embodiment of the present invention, cathodal stimulation308 is of a duration less than 0.3 milliseconds and at a voltage greaterthan twenty volts. In another alternative embodiment, anodal stimulation302 is administered over 200 milliseconds post heart beat. In the mannerdisclosed by these embodiments, as well as those alterations andmodifications which may become obvious upon the reading of thisspecification, a maximum membrane potential without activation isachieved in the first phase of stimulation.

FIG. 4 depicts biphasic electrical stimulation wherein a firststimulation phase comprising anodal stimulation 402 is administered overperiod 404 with rising intensity level 406. The ramp of rising intensitylevel 406 may be linear or non-linear, and the slope may vary. Thisanodal stimulation is immediately followed by a second stimulation phasecomprising cathodal stimulation 408 of conventional intensity andduration. In an alternative embodiment of the invention, anodalstimulation 402 rises to a maximum subthreshold amplitude. In yetanother alternative embodiment of the invention, anodal stimulation 402rises to a maximum amplitude that is less than three volts. In anotheralternative embodiment of the invention, anodal stimulation 402 is aduration of approximately two to eight milliseconds. In yet anotheralternative embodiment of the invention, cathodal stimulation 408 is ofa short duration. In another alternative embodiment of the invention,cathodal stimulation 408 is approximately 0.3 to 1.5 milliseconds. Inyet another alternative embodiment of the invention, cathodalstimulation 408 is of a high amplitude. In another alternativeembodiment of the invention, cathodal stimulation 408 is in theapproximate range of three to twenty volts. In yet another alternativeembodiment of the present invention, cathodal stimulation 408 is of aduration less than 0.3 milliseconds and at a voltage greater than twentyvolts. In another alternative embodiment, anodal stimulation 402 isadministered over 200 milliseconds post heart beat. In the mannerdisclosed by these embodiments as well as those alterations andmodifications which may become obvious upon the reading of thisspecification, a maximum membrane potential without activation isachieved in the first phase of stimulation.

FIG. 5 depicts biphasic electrical stimulation wherein a firststimulation phase comprising series 502 of anodal pulses is administeredat amplitude 504. In one embodiment rest period 506 is of equal durationto stimulation period 508 and is administered at baseline amplitude. Inan alternative embodiment, rest period 506 is of a differing durationthan stimulation period 508 and is administered at baseline amplitude.Rest period 506 occurs after each stimulation period 508 with theexception that a second stimulation phase comprising cathodalstimulation 510 of conventional intensity and duration immediatelyfollows the completion of series 502. In an alternative embodiment ofthe invention, the total charge transferred through series 502 of anodalstimulation is at the maximum subthreshold level. In yet anotheralternative embodiment of the invention, the first stimulation pulse ofseries 502 is administered over 200 milliseconds post heart beat. Inanother alternative embodiment of the invention, cathodal stimulation510 is of a short duration. In yet another alternative embodiment of theinvention, cathodal stimulation 510 is approximately 0.3 to 1.5milliseconds. In another alternative embodiment of the invention,cathodal stimulation 510 is of a high amplitude. In yet anotheralternative embodiment of the invention, cathodal stimulation 510 is inthe approximate range of three to twenty volts. In another alternativeembodiment of the invention, cathodal stimulation 510 is of a durationless than 0.3 milliseconds and at a voltage greater than twenty volts.The individual pulses of the series of pulses may be square waves, orthey may be of any other shape, for example, pulses which decay linearlyor curvilinearly from an initial subthreshold amplitude, to a loweramplitude.

In the preferred biphasic stimulation protocol practiced by the presentinvention, the magnitude of the anodal phase does not exceed the maximumsubthreshold amplitude. The anodal phase serves to precondition thestimulated myocardium, thereby lowering the excitation threshold suchthat a cathodal stimulation of lesser intensity than normal will producedepolarization leading to contraction.

The values of duration and amplitude will depend on factors such as theplacement/position of the particular electrode (including, e.g., whetherthe electrode is in purely muscle tissue versus in specializedconducting or pacemaking tissue), whether damaged/scarred tissue is inclose vicinity to the electrode, depth of the electrode within thetissue, local tissue resistance, presence or absence of any of a largerange of local pathologies, etc. Nonetheless, typical anodal phasedurations often fall within the range from about two milliseconds toabout eight milliseconds, whereas typical cathodal durations often fallwithin the range from about 0.3 millisecond to about 1.5 millisecond.Typical anodal phase amplitudes (most commonly at the maximumsubthreshold amplitude) often fall within the range from about 0.5 voltto 3.5 volts, compared to typical cathodal phase amplitudes from about 3volts to about 20 volts.

The present invention also permits the physician to readily test rangesof stimulation and other parameters (voltage, duration, shape of voltageversus time pulses, etc.) once the anti-reentry system is in place inthe patient. Thus, the ability to engage in trial and error testing ofpulsing parameters permits the physician not only to determine such aparameter as maximum subthreshold amplitude, but also to optimize otherstimulation parameters to fit a given patient's condition, location ofelectrodes, etc. Furthermore, the physician may so determine optimalparameters for each individual electrode in a set of multipleelectrodes.

Such a system of testing could be related to defibrillation thresholdtesting, wherein ventricular fibrillation is deliberately provoked andvarious levels of defibrillatory shocks are given to determine theamount of energy needed. In the present application, testing is donewith the various patterns of pacing so as to find the one with thelowest requirement for countershock energy.

Based on the examples provided herein, the skilled practitioner in theart will readily appreciate that generalization of the teachings expandsthe scope of the present invention to include stimulation time andvoltage ranges to beyond those mentioned herein, as well as to beyondthe numbers of individual electrodes employed, and other parameterssubject to simple and quick experimentation in a specific situation notspecifically addressed in the verbiage presented on the practice of thepresent invention.

Having thus described the basic concept of the invention, it will bereadily apparent to those skilled in the art that the foregoing detaileddisclosure is intended to be presented by way of example only, and isnot limiting. Various alterations, improvements and modifications willoccur and are intended to those skilled in the art, but are notexpressly stated herein. These modifications, alterations andimprovements are intended to be suggested hereby, and within the scopeof the invention. Accordingly, the invention is limited only by thefollowing claims and equivalents thereto.

What is claimed is:
 1. An apparatus for applying biphasic myocardialstimulation, the apparatus comprising: at least two electrodes adaptedto administer biphasic stimulation to myocardial tissue; and a pacemakerconnected to provide biphasic stimulation to the at least twoelectrodes, wherein the biphasic stimulation comprises: a firststimulation phase having a first phase polarity, a first phaseamplitude, a first phase shape, and a first phase duration, so as toprecondition the myocardium to accept subsequent stimulation, and asecond stimulation phase having a second phase polarity, a second phaseamplitude that is larder in absolute value than the first phaseamplitude, a second phase shape, and a second phase duration; andwherein the pacemaker repeatedly provides biphasic stimulation so longas fibrillation is detected.
 2. The apparatus for applying myocardialstimulation according to claim 1, wherein the first phase polarity ispositive, and the second phase polarity is negative.
 3. The apparatusfor applying myocardial stimulation according to claim 2, wherein thefirst phase amplitude is at a maximum subthreshold amplitude.
 4. Theapparatus for applying myocardial stimulation according to claim 3,wherein the maximum subthreshold amplitude is about 0.5 volt to about3.5 volts.
 5. The apparatus for applying myocardial stimulationaccording to claim 1, wherein the first phase shape is ramped from abaseline value to a second value.
 6. The apparatus for applyingmyocardial stimulation according to claim 5, wherein the second value isnot more than a maximum subthreshold amplitude.
 7. The apparatus forapplying myocardial stimulation according to claim 1, wherein the firstphase duration is about one millisecond to about nine milliseconds. 8.The apparatus for applying myocardial stimulation according to claim 1,wherein the second phase amplitude is about two volts to about twentyvolts.
 9. The apparatus for applying myocardial stimulation according toclaim 1, wherein the second phase duration is about 0.2 millisecond toabout 1.5 milliseconds.
 10. The apparatus for applying myocardialstimulation according to claim 1, wherein the first stimulation phasefurther comprises a series of stimulating pulses of a predeterminedamplitude and duration, and a series of rest periods.
 11. The apparatusfor applying myocardial stimulation according to claim 10, whereinapplying the first stimulation phase further comprises applying a restperiod after at least one stimulating pulse.
 12. The apparatus forapplying myocardial stimulation according to claim 10, wherein thepredetermined duration is about 0.2 millisecond to about 1.5milliseconds.
 13. The apparatus for applying myocardial stimulationaccording to claim 10, wherein the rest period is about 0.2 millisecondto about 1.2 milliseconds.
 14. The apparatus for applying myocardialstimulation according to claim 1, wherein the first phase shape isselected from the group consisting of: square wave pulse, ramped pulse,and series of short duration square wave pulses.
 15. The apparatus forapplying myocardial stimulation according to claim 1, wherein at leastone of the electrodes is adapted for application to an inner ventricularwall via the vena cava.
 16. The apparatus for applying myocardialstimulation according to claim 1, wherein at least one of the electrodesis adapted for application to an exterior ventricular wall.
 17. Theapparatus for applying myocardial stimulation according to claim 1,wherein the stimulation is applied to the electrodes progressively in amanner that mimics the normal flow of electrical depolarization in aheart.
 18. The apparatus for applying myocardial stimulation accordingto claim 17, wherein the electrodes closest to the A-V node are thefirst to administer stimulation, wherein the electrodes farthest fromthe A-V node, following the normal intrinsic conduction paths, are thelast to administer stimulation; and wherein the electrodes intermediatebetween the electrodes closest to the A-V node and the electrodesfarthest from the A-V node each administer stimulation at anintermediate time that is proportional to their intermediate position,following the normal intrinsic conduction paths.
 19. The apparatus forapplying myocardial stimulation according to claim 18, wherein theelectrodes are ordered by class according to their distance from the A-Vnode, following the normal intrinsic conduction paths.
 20. The apparatusfor applying myocardial stimulation according to claim 19, wherein thenumber of classes is between two and about thirty.
 21. The apparatus forapplying myocardial stimulation according to claim 1, wherein the firststimulation phase comprises an anodal stimulus.
 22. A cardiacstimulation apparatus for reverting ventricular arrhythmias withbiphasic waveforms, the apparatus comprising: at least two electrodesadapted to administer biphasic stimulation to cardiac tissue, whereinthe biphasic stimulation comprises: a first stimulation phase having apositive polarity, a subthreshold amplitude, a duration of about onemillisecond to about nine milliseconds, and a shape, wherein the shapeis selected from the group consisting of: square wave pulse, rampedpulse, and series of short duration square wave pulses; and a secondstimulation phase having a negative polarity, an amplitude of about twovolts to about twenty volts that is larger in absolute value than thefirst stimulation chase subthreshold amplitude, and a duration of about0.2 millisecond to about 1.5 milliseconds.